newton laws of motion

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  • 1. Physics project
    Done by,
    R.Sri Krishna
    IXth CBSE
    Roll no :- 21
    Nalanda Talent School

2. Newtons Laws of Motion
3. A Brief Introduction.
Newton's laws of motionconsist of threephysical lawsthat form the basis forclassical mechanics. They describe the relationship between the forces acting on a body and itsmotiondue to those forces. They have been expressed in several different ways over nearly three centuries.
The three laws of motion were first compiled bySir Isaac Newtonin his workPhilosophi Naturalis Principia Mathematica, first published on July 5, 1687. Newton used them to explain and investigate the motion of many physical objects and systems
4. Newton's First and Second laws, in Latin, from the original 1687 edition of thePrincipia Mathematica.
5. Newtons first law of motion (law of inertia)
6. First law of motion
First law of motion :- Every body remains in a state of rest or uniform motion (constantvelocity) unless it is acted upon by an external unbalanced force.This means that in the absence of a non-zero net force, thecenter of massof abodyeither remains at rest, or moves at a constantspeedin a straight line.
This tendency is also known as inertia!
7. Inertia
Inertia is thetendency of an object to resist changes in its velocity. whether in motion or not
The ball doesn't move unless it is acted upon by an external unbalanced force.
8. Dont let this be you. Wear seat belts.
Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour, so it moves forward!!!
Newtons 1st law and you
9. Now we can get a doubt that
What is this unbalanced force that acts on an object in motion?
It is none other than friction!! Once airborne or in motion, unless acted on by an unbalanced force (gravity and air fluid friction), it would never stop!
10. For example --- Unless acted upon by an unbalanced force, this golf ball move forever. But because friction and gravity are acting on it the ball is stopping!
11. Newtons second law of motion
12. Momentum
Momentum of a body is defined as the product of its mass and velocity
P(momentum) = M(mass) x V(velocity)
13. Second law of motion
The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force
14. Thistell us that :-
Force = Mass x acceleration
15. Units
When mass is in kilograms and acceleration is in m/s*s the unit of force is in Newton (N). One Newton is equal to the force required to accelerate one kilogram of mass at one meter/second square
16. If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.
17. Newtons 2nd Lawproves that different masses accelerate to the earth at the same rate, but with different forces
We know that objects with different masses accelerate to the ground at the same rate.
However, because of the 2nd Law we know that they dont hit the ground with the same force.
F = ma
9.8 N = 1 kg x 9.8 m/s/s
F = ma
98 N = 10 kg x 9.8 m/s/s
18. Newtons 3rd law of motion
19. Third law of motion
For every action, there is an equal and opposite reaction.
This may be the most popularlaw in the universe !
This law is sometimes referred to as theaction-reaction law, withFcalled the "action" and Fthe "reaction". The action and the reaction are simultaneous.
20. Conservation of momentum
According to Newton's third law every action has an equalantreaction in the opposite direction .
So, when 2 bodies of masses M1 and M2 collide with initial velocities U1 and U2 in a time period t ,Then -
Force of A on B = -(Force of B on A )
=>M1(V1-U1)/t = M2(V2-U2)/t
=>M1U1 +M2U2 = -(M1V1 + M2V2)
21. Examples
According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
22. There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.

  • Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards.In turn, the water reacts by pushing the fish forwards, propelling the fish through the water.

24. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).